theory

Question 1

What do you call the program that runs Java byte-code instructions

Answer 1

interpreter

Question 2

scanner take input from text file

Answer 2

Scanner fileIn = new Scanner(new FileInputStream(“data.txt”)

Question 3

Programmers of robots need to ensure?

Answer 3

the robot does not harm humans
the robot obeys orders
the robot protects itself

Question 4

moral agency

Answer 4

Moral agency requires that all three criteria of causality, knowledge and
choice apply to the agent/person involved

Question 5

Categorical Imperative

Answer 5

fundamental principle behin deontology

Question 6

static variable

Answer 6

variable that belongs to the class as a whole, and not just to one object
▪ There is only one copy of a static variable per class, unlike instance variables where each object has its own copy
▪ All objects of the class can read and change a static variable
▪ Although a static method (discussed shortly) cannot access an instance variable, a static method can access a static variable
▪ A static variable is declared like an instance variable, with the addition of the modifier static
static variable should always be defined private, unless it is also a
defined constant
value cannot be altered
In addition to static, the declaration for a static defined constant must include modifier final, which indicates that its value cannot be changed
▪ When referring to such a defined constant outside its class, use the name of its class in place of a calling object
Static variables in base class are inherited by any of its derived classes

Question 7

data type default values

Answer 7

boolean static variables are initialized to false
Other primitive types static variables are initialized to the zero of their type
▪ Class type static variables are initialized to null

Question 8

static methods

Answer 8

one that can be used without a calling object
▪ A static method still belongs to a class, and its definition is given inside the class definition
Static methods are invoked using the class name in place of a calling
object
static method cannot refer to an instance variable of the
class, and it cannot invoke a nonstatic method of the class
has no this, so it cannot use an instance variable or
method that has an implicit or explicit this for a calling object

Question 9

wrapper classes

Answer 9

provide a class type corresponding to each of the primitive types
▪ This makes it possible to have class types that behave somewhat like
primitive types
▪ The wrapper classes for the primitive types byte, short, long,
float, double, and char are (in order) Byte, Short, Long, Float, Double, and Character
▪ Wrapper classes also contain a number of useful predefined
constants and static methods

have static methods to convert: eg Integer.parseInt , Double.toString, Character.toUpperCase(char)

Question 10

boxing

Answer 10

process of going from a value of a primitive type to an object of its wrapper class
▪ To convert a primitive value to an “equivalent” class type value, create
an object of the corresponding wrapper class using the primitive value as an argument
▪ The new object will contain an instance variable that stores a copy of the primitive value
▪ Unlike most other classes, a wrapper class does not have a no-
argument constructor

Question 11

unboxing

Answer 11

process of going from an object of a wrapper class to the corresponding value of a primitive type
▪ The methods for converting an object from the wrapper classes Byte, Short, Integer, Long, Float, Double, and Character to their
corresponding primitive type are (in order) byteValue, shortValue,
intValue, longValue, floatValue, doubleValue, and charValue
▪ None of these methods take an argument
int i = integerObject.intValue()

Question 12

secondary vs main memory

Answer 12

2nd: hold files for permanent storage
main: used by computer program when it is running a program, keeps values stored in program’s variables

Question 13

bytes

Answer 13

long list of numbers for location
contains 8 bits
data item can be stored in byes
identified by a number called its address, used to find the data when its needed

Question 14

memory location

Answer 14

entire chunk of memory that holds data
address of the first byte of this memory location is used as the
address for the data item

Question 15

storing primative variables

Answer 15

When the variable is a primitive type, the value of the variable
is stored in the memory location assigned to the variable
Each primitive type always require the same amount of memory to
store its values

Question 16

storing class type variables

Answer 16

When the variable is a class type, only the memory address (or
reference) where its object is located is stored in the memory location
assigned to the variable
The object named by the variable is stored in some other location in memory
value of class variable is a fixed size
the value of a class variable is a memory address or reference
object can be any size

Question 17

references

Answer 17

Two reference variables can contain the same reference, and
therefore name the same object
The assignment operator sets the reference (memory address) of one
class type variable equal to that of another
Any change to the object named by one of theses variables will
produce a change to the object named by the other variable, since
they are the same object
variable2 = variable1;

Question 18

paramters gen

Answer 18

call-by-value parameters
▪ A parameter is a local variable that is set equal to the value of its
argument
▪ Therefore, any change to the value of the parameter cannot change
the value of its argument

Question 19

class parameters

Answer 19

value plugged into a class type parameter is a reference
(memory address)
▪ Therefore, the parameter becomes another name for the argument
▪ Any change made to the object named by the parameter (i.e.,
changes made to the values of its instance variables) will be made
to the object named by the argument, because they are the same
object
▪ Note that, because it still is a call-by-value parameter, any change
made to the class type parameter itself (i.e., its address) will not
change its argument (the reference or memory address)

Question 20

primitive vs class type parameters

Answer 20

A method cannot change the value of a variable of a primitive type that is an argument to the method
▪ In contrast, a method can change the values of the instance variables of a class type that is an argument to the method

Question 21

== vs equals

Answer 21

== checks that two class type variables have the same memory addres
Two objects in two different locations whose instance variables have exactly the same values
would still test as being “not equal”

Question 22

defensive copying

Answer 22

The private modifier only prevents direct field access—it doesn’t prevent indirect modification through shared object references

this.birthDate = new Date(birthDate.getTime());

use copy rather then actual reference which can create data leaks

Question 23

copy constructor

Answer 23

constructor with a single argument of the same type as the class

should create an object that is a
separate, independent object, but with the instance variables
set so that it is an exact copy of the argument object
creates completely new and independent copy

check null then if not assign variables from parameter to this

Question 24

immutable class

Answer 24

A class that contains no methods (other than constructors) that
change any of the data in an object of the class is called an
immutable class

Objects of such a class are called immutable objects

safe to return a reference to an immutable object

object cannot be changed in any way
the contents of an immutable object cannot be modified.
immutable object contains no mutator methods.

Question 25

mutable class

Answer 25

A class that contains public mutator methods or other public methods that can change the data in its objects is called a mutable class, and its objects are called mutable objects Never write a method that returns a mutable object ▪ Instead, use a copy constructor to return a reference to a completely independent copy of the mutable object

Question 26

deep vs shallow copy

Answer 26

A deep copy of an object is a copy that, with one exception, has no references in common with the original : References to immutable objects are allowed to be share Any copy that is not a deep copy is called a shallow copy ▪ This type of copy can cause dangerous privacy leaks in a program

Question 27

array

Answer 27

data structure used to process a collection of data that is all of the same type ▪ An array behaves like a numbered list of variables with a uniform naming mechanism ▪ It has a part that does not change: the name of the array ▪ It has a part that can change: an integer in square bracket

Question 28

classes

Answer 28

Every program is a class All helping software consists of classes All programmer-defined types are classe

Question 29

new

Answer 29

new operator must be used to create the object and associate it with its variable name

Question 30

array - call by reference

Answer 30

any changes you make to array are permanent changes The parameter becomes another name for the argument ▪ Any change made to the object named by the parameter (i.e., changes made to the values of its instance variables) will be made to the object named by the argument, because they are the same object any change made to the class type parameter itself (i.e., its address) will not change its argument (the reference or memory address

Question 31

infornation hiding

Answer 31

practice of separating how to use a class from the details of its implementation

Question 32

abstraction

Answer 32

another term used to express the concept of discarding details in order to avoid information overloa

Question 33

@Override

Answer 33

ensures method is an override and not an overload

Question 34

encapsulation

Answer 34

data and methods of a class are combined into a single unit (i.e., a class object), which hides the implementation details ▪ Knowing the details is unnecessary because interaction with the object occurs via a well-defined and simple interface In Java, hiding details is done by marking them private

Question 35

overloading & overriding

Answer 35

overriding- subclass provides a specific implementation for a method that is already defined in the superclass. inheritance . exact same number and types of parameters as in base class overloading: multiple methods in the same class with the same name but have different numbers of parameters. It allows to perform operations with different inputs. two or more methods in the same class can be derived, diff signature from method in base class

Question 36

is a

Answer 36

inheritance derived class not aggregation or composition

Question 37

has a

Answer 37

composition occurs when a class contains an instance variable of a class type does not denote polymorphism

Question 38

driver program

Answer 38

A program whose only purpose is to test a method

Question 39

bottom up testing

Answer 39

One method often invokes other methods, so one way to do this is to first test all the methods invoked by that method, and then test the method itself

Question 40

a stub

Answer 40

Sometimes it is necessary to test a method before another method it depends on is finished or tested. In this case, use a simplified version of the method, called a stub, to return a value for testing

Question 41

The Fundamental Rule for Testing Methods

Answer 41

Every method should be tested in a program in which every other method in the testing program has already been fully tested and debugged

Question 42

method signature

Answer 42

signature consists of the name of a method together with its parameter list does not include the type returned

Question 43

class definition

Answer 43

specifies the data items (properties) and methods (actions) that all of its objects will have Data items and methods are sometimes called members of the object Data items are called fields or instance variables

Question 44

local variable

Answer 44

variable declared within a method definition All variables declared in the main method are local All method parameters are local variable

Question 45

call by value mechanism

Answer 45

the value of each argument (not the variable name) is plugged into the corresponding method parameter' plugging in arguments for formal parameters any change to the value of the parameter cannot change the value of its argument

Question 46

boolean default

Answer 46

false

Question 47

primitive default

Answer 47

0

Question 48

equals

Answer 48

== :checks for reference equality, meaning it only returns true if both references point to the same memory location. .equals() check for value equality appropriate for comparing content of objects

Question 49

memory in computer

Answer 49

Secondary memory is used to hold files for "permanent" storage Main memory is used by a computer when it is running a program

Question 50

main memory

Answer 50

consists of a long list of numbered locations called bytes Each byte contains eight bits: eight 0 or 1 digits the entire chunk of memory (several adjacent bytes) that holds the data is called its memory location The address of the first byte of this memory location is used as the address for the data item

Question 51

address

Answer 51

number that identifies a byte A data item can be stored in one (or more) of these bytes ▪ The address of the byte is used to find the data item when needed

Question 52

primitive references

Answer 52

When the variable is a primitive type, the value of the variable is stored in the memory location assigned to the variable Each primitive type always require the same amount of memory to store its value

Question 53

class references

Answer 53

When the variable is a class type, only the memory address (or reference) where its object is located is stored in the memory location assigned to the variable ▪ The object named by the variable is stored in some other location in memory The value of a class variable is a fixed size The value of a class variable is a memory address or reference ▪ The object, whose address is stored in the variable, can be of any size

Question 54

Differences Between Primitive and Class-Type Parameters

Answer 54

A method cannot change the value of a variable of a primitive type that is an argument to the method ▪ In contrast, a method can change the values of the instance variables of a class type that is an argument to the method

Question 55

final

Answer 55

method may not be redefined in derived class class may not be used as a base class to derive other classes

Question 56

types of derived object

Answer 56

An object of a derived class has type of the derived class, and it also has type of the base class has the type of every one of its ancestor classes object of derived class can be assigned to variable of any ancestor type can be used anyplace that an object of any of ancestor types can be used (NOT vice versa)

Question 57

Object

Answer 57

every class is a descendent of the class Object equals toString

Question 58

overriden equals

Answer 58

The parameter otherObject of type Object must be type cast to the given class (e.g., Employee) However, the new method should only do this if otherObject really is an object of that class, and if otherObject is not equal to null Finally, it should compare each of the instance variables of both objects

Question 59

getClass vs instancof

Answer 59

The instanceof operator simply tests the class of an object true if object is an instance of class or any subclass The getClass() method used in a test with == or != tests if two objects were created with the same class getClass more restrictive, doesnt care abt inheritance

Question 60

Circle x = new Circle(),

Answer 60

x contains a reference to a Circle object.

Question 61

privacy leak

Answer 61

A condition that allows a programmer to circumvent the private modifier and change the private instance variable

Question 62

default value of uninitialized boolean

Answer 62

false

Question 63

Java features that ensure platform independence or security

Answer 63

bytecode no direct memory access java virtual machine (JVm)

Question 64

overriden methods in subclass

Answer 64

When a method is overridden in a subclass, it can be made MORE visible and its return type can be made more SPECIALISED (meaning its return type can be a DESCENDANT of the type in the parent's method)

Question 65

visibility of modifers in order

Answer 65

private, default (if no modifier is used), protected, and public

Question 66

which is ideal for a use case where several classes share functionality and have partial overlap in implementations?

Answer 66

abstract classes

Question 67

static methods

Answer 67

Static variable- belongs to class Only one copy per class - all objects of that class refer to that static variable Static method : - cannot access instance variable - can access static variable - cannot invoke a non-static method of the class - can invoke another static method It is always preferable to explicitly initialize static variables rather than rely on the default initialization static variable should always be defined private, unless it is also a defined constant Static methods are invoked using the class name in place of a calling object

Question 68

non static inner class

Answer 68

A non-static inner class cannot be created without an instance of the outer class

Question 69

int a =7; int b =2; double c = a/b; System.out.println(c); output?

Answer 69

3.0 does integer division

Question 70

User experience design is an important part of user interface design.

Answer 70

False

Question 71

User interface design is an important part of user experience design.

Answer 71

True